I'm not picking on Paul, this is just a handy place to reply. I'm going to say this one more time (the first time was two years ago).
I really don't understand all of the fuss about 1 Hz accuracy when just changing the K3 Width and Shift controls moves the frequency more than that and this is band dependent. On ten-meters I can listen to a crystal-controlled source and hear the beat note change as Shift and Width are adjusted. Elecraft considers its frequency conversion scheme to be proprietary but it's obvious that not all of the oscillators are moving at the same rate. Wes N7WS --- On Sat, 3/19/11, Paul Christensen <w...@arrl.net> wrote: > I installed it on Friday in about 30 > minutes, but I'm comfortable with my > way around the K3. I would think that most users > could install it in about > an hour or less. Installation is actually very simple > with very few parts > involved. K3EXREF came with an SMA connector and SMA > to BNC between-series > adapter. > > Performance is exactly as promised by Elecraft. > Although K3EXREF will not > phase lock the K3 to the external frequency source, I'm > finding that it > stays within 1 Hz on 20m when locked to CHU at 14.670 > MHz. I'm also > finding that testing for zero-beat to WWV at 10 MHz is not > a good idea in my > shack, and perhaps yours too. There are many 10 MHz > signals being emitted > by nearby appliances, LAN routers, security system, > Ethernet boards, etc. > That common, even frequency is everywhere in a household > these days. > > In much of North America, CHU is an excellent source for > testing since it > keeps cesium accuracy like WWV but the odd frequency of CHU > is a real > benefit since the chance for beating against extraneous > signals is much > smaller than at 10 MHz. Testing at a higher frequency > rather than say the > MW broadcast band also provides for a reasonably good > account of how the > K3EXREF performs. After installation, I > would also suggest not trying to > test zero beat K3EXREF against commercial MW or SW BC > stations since their > carriers are allowed to deviate much more than the > cesium-based time and > frequency standards of CHU and WWV. Commercial AM > broadcast station > frequencies are typically only accurate to about +/- 20 Hz > although most are > better than that. > > The K3's 49 MHz oscillator is only adjusted at intervals > between 4 and 8 > seconds by K3EXREF in order to minimize jitter. The > K3 retains its original > phase noise performance since the external reference is not > used internal to > the K3's frequency generating scheme. Think of it > this way -- K3EXREF is > like lightly touching the 49 MHz oscillator with a feather > every few seconds > if necessary to keep it within 1 Hz or so. Also, the > K3 frequency stays > accurate even at the moment of powering up the K3. > Kinda' fun to watch the > 49 MHz oscillator display change during warm-up as it's > being corrected and > compared against the external reference. > > External references: There are three primary types, > and all can be > purchased for less than USD $150 on the used market. > Cesium standards (a > fourth type) are also available but are generally much more > expensive, > complicated, and won't offer any benefit to K3 users since > K3EXREF limits > resolution and accuracy to about 1 Hz. > > The first type is the GPS Disciplined Oscillator > (GPS-DO). This type of > standard locks itself onto the visible GPS satellites > orbiting the sky. > Requires a GPS antenna and is self-calibrating to the GPS > satellites. The > GPS-DO's time and frequency averages from the visible > satellites, each > satellite having it's own on-board cesium-based > oscillator. Long-term > accuracy is usually good to at least 1 x 10^-11. > Extreme accuracy and only > a magnitude or two behind cesium. Look for > Hewlett-Packard Z3801A, Z3816A, > Trimble Thunderbolt, Brandywine, Symmetricon, and Datum > models. Short list, > but many others available. > > Rubidium is the next type. No GPS tracking > needed. Accuracy commensurate > with GPS-DO. No antenna required. Long-term > performance is highly > dependent on the quality of the optical beam from the > rubidium pump lamp. > Look for EF Efratom, Datum, > > Third, is a high quality oven-controlled crystal oscillator > (OCXO). > Requires periodic calibration. Accuracy good to at > least +/- 0.05 ppm and > offer the best phase noise performance among the three > types of oscillators, > but as noted earlier, the excellent phase noise attributes > of the OCXO will > not be carried over to the K3. > > A shack reference oscillator is good for use with other > equipment too (e.g., > frequency counter). Although a bit lossy, > I currectly use a Mini-Circuits > passive three-way splitter, but one can purchase a > distribution amp to feed > many pieces of equipment from a single oscillator. > Unlike the splitter, a > DA offers unity gain and very high port isolation. > > Finally, be mindful that most GPS-DO and rubidium units use > internal > switch-mode DC-DC converters. Switching noise was bad > enough on two of my > units that I decided to gut the converters and used an > outboard > triple-output linear supply. The Trimble Thunderbolts > that have been > retired from the cellular industry require an external > triple-output supply. > If choosing this model, get a linear type and avoid the > headaches. > > Paul, W9AC > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
